Method of cracking hydrocarbon oils



@Fuy H9, i938. Q H. c. PENNRICH 2,323,960

METHOD OF CRACKING HYDBOCRBON OILS l Filed Aug. 29, 1935 Separor Ceo/@r.y Dlsl/laion Tower y Tar Flash Tawer 4:

` Fresh'eed Frasi? Fed 2 kIl QQIa 2l .n

Cracking l Zone @as s @Il Healng l2 Haarmg 2mm I7 Z one INVENToR.

Henry C. Pennrlch.

Patented July 1.9, 1938 2,123,960 METHOD F CRACKIG HYDROCARBON Henry C.Pennrlch,-Brussels, Belgium Application August 29, 1935, Serial No.38,362

Claims.

This invention relates to the cracking of hydrocarbon oils and it refersmore particularly to the production of motor fuels having high antiknockvalues.

In my former applications, Serial No. 610,346, originally led May 10,1932 and Serial No. 633,551, led September 17, 1932, a method ofcracking hydrocarbon oils is disclosed, in which normally incondensablehydrocarbon gases, obtained as a byproduct of the cracking and followingdistillation of hydrocarbon oils, are subjected to high pressure andtemperature and are admixed to the fresh charge oil to be cracked underconditions wherein the reaction time and temperature of the oil crackingprocess are carefully controlled. An improved gasoline is thus producedat a distinctly higher yield and with considerably lower gas formation.

Under the above conditions, many of the compounds present in the crackedgases undergo conversion and form normally liquid hydrocarbons. Thisconversion is generally the result of the polymerization of unsaturatedhydrocarbons present or formed from saturated constituents by thecracking reaction. These normally incondensable gases, obtainedcoincident with the cracking operation, contain the compounds butane,propane, ethane and the corresponding unsaturated hydrocarbons as wellas the so-called xed gases methane, hydrogen, carbon monoxide and carbondioxide. It is generally found that the fixed gasesare highly stable andgenerally that they do not readily undergo conversion under the aboveconditions and thus it is found that through the presence of the xedgases the conversion of the higher boiling compounds becomes incomplete.

Based on these observations I found it highly advantageous to remove thefixed gases from the cracked gases before they are compressed and heatedfor admixture and to subject only the remaining higher boilingincondensable hydrocarbons to higher pressure and temperaturewherethrough they-are very readily and completely converted and thusthey then form the valuable products as Yrequired for the Aaboveindicated purpose. 4

Thus when the highly stable or the xed gases methane, hydrogen etc. areabsent, then the products in the remaining mixture are present at higherconcentrations and `for that reason the conversion will naturallyproceed further giving a greater yield of liquid products. Theseconversion products may be formed either from the gas constituents aloneor they may be reaction products from these and the fresh hydrocarbonoil products with which they are mixed. In general, the results of thisprocess are a greater gasoline yield, less gas formation and a smootherreaction and performance of the cracking proc- 5 ess; this may in partalso be attributed to the' greater amount of heat available due to theexothermic character of the reaction of polymerization and the morehighly concentrated gas mixture.

'I'he method of 'separating the low molecular or fixed gas constituentsfrom the cracked gases' can be carried out in a variety of ways but inpractice the following process was found to be most convenient andeconomical. A mixture of vgasoline and cracked gases obtained bydistillation is brought toa pressure of about 150 pounds per square inchand a temperature at which the gasoline is completely liquefied. Underthese conditions, the higher boiling gas constituents are dissolvedwhile a gas 4rich in methane and hydrogen remains unabsorbed and `isremoved. The solution is then heated whereby the dissolved gasconstituents are again set free. They are compressed, heated and passedon into the principal cracking unit.

One example of a practical unit embodying` the features of my inventionis illustrated in the accompanying drawing and it is to be operated asfollows: 30 The fresh feed, such as a crude oil or products obtainedfrom crude oils and similar products, enters through pipe I and is mixedwith the cracked products at point 2 and from there the mixture is sentinto the flash tower 3. Heavy tar and overhead vapors are separated fromthe mixture by condensation in the tower and it is continuouslywithdrawn from the bottom by means of pipe 4. The overhead vapors arepassed by means of pipe 5 'into the distilling tower 6. A condensateconsisting mainly of gas oil is collected .in the cooler 8 and is sentto the separator 9. The separator contains gasoline as a solvent for thehigher molecular compounds and is operated at a pressure of ,150 poundsper square inch 'and a gas is. separated from the liquid. This gascomprises the xed'gases .and consists of methane, hydrogen, CO and CO2and is withdrawn by means of pipe I3. The liquid is -sent into thesecond separator. I0 by means of pipe I4, in which the liquid is heatedto around '300 F. under substantially the samek pressure. The heating isobtained by the use of steam circulating through the steam coil 22. Astabilized gasoline is' withdrawn into the storage tank by 55 means ofpipe 23 and a gas is taken from the top of the stabilizer or separator.This gas contains the hydrocarbons ethane, propane, butane and thecorresponding unsaturates. The gas is recycled through pipe I5 and itspressure is increased to around 1000 pounds per square inch before thegas enters the heating zone I6.

In the heating zone consisting of tubes placed in a furnace thetemperature of the recycle gas is raised to around 1050 F. The heatedgas is sent into the oil cracking zone I9 by means of. the

pipe I8. The pipe I1 is a bypass and contains.

the control valve 20.

The condensate of the distillation tower 6 leaving by way of pipe 'I iscompressed to around 1000 pounds per square inch. Additional distillatescan be added to this stream by way of pipe II. The stream enters the oilheating zone I2 which consists of tubes placed in a furnace. In thiszone, the temperature of the oil is raised to around 800 F.

The heated oil of zone I2 is mixed with the heated gas of zone I 6 inproportion to obtain a temperature of between 840 and 880 F. The mixtureis passed through the oil cracking zone I9 consisting of tubes placed ina furnace. The

. furnace is only moderately heated in order to replace the heat lostduring the course of the cracking process. Additional amounts of gas mayalso be added into the cracking zone at various intermediate pointsalong zone I9 which are not shown. The cracking zone is made sumcientlylong to assure a cracking time of around 10 minutes. The temperature ofthe oil gas mixture at the beginning and at the end of this zone areabout the same. 'I'he products leaving the crackingzone are decreased inpressure by means of pressure valve 2i and from then on the pressurewill be around 200 pounds per square inch. The products are mixed withfresh charge oil entering through pipe I whereby the temperature isbrought to about '700 F. and then the mixture is sent to the flash tower3.

The conditions of pressure and temperature may vary from those givenabove according to the type and kind of oil to be converted and theproducts desired. In general, in the heating and the cracking zones, thepressure may be between 300 and 3000 pounds per square inch while thepressures in all other parts of the operation such as in thedistillation vand separation tower should be below 300 pounds per squareinch. The temperature of the oil cracking zone is to range between 840and 960 F. for most of the stocks, while in the gas heating zone it isto be still lower than these temperatures.

Having thus described one typical example of my process, I do not bindmyself to the exact details given in the above description, but ratherconsider this as one example illustrating the general broad idea ofmyinvention.

I claim:-

1. The method of cracking hydrocarbon oils comprising the steps ofseparating normally incondensible hydrocarbon gases into a nrs-t'fraction rich'in methane and into a second fraction substantially freefrom methane. heating said second fraction under a-pressure of between500 and 3000 pounds per square inch to a temperature sufficient to startexothermic polymerization and not exceeding 1200 F., and keeping saidteml perature substantially constant whereby a fully controlledpolymerization product is obtained.`

drocarbon oil to be cracked, said hydrocarbon oil being heated to atemperature below its cracking temperature and said mixture being inproportions suflicient to cause cracking of apart of said oil, passingsaid mixture through a cracking zone, and maintaining said pressure onsaid mixture in the cracking zone, removing the mixture from thecracking zone andadding cold fresh feed to the cracking mixture.

2. The method of cracking hydrocarbon oils to obtain a high-gradeanti-knock motor fuel comprising the steps of separating from normallyincondensible hydrocarbon gases the fixed gases methane, carbon monoxideand dioxide. ethane, nitrogen, hydrogen etc., subjecting the remainingnormally incondensible hydrocarbon gases to a pressure between 500 and3000 pounds per square inch and to a temperature to start polymerizationbut not exceeding 1200 F., and,

maintaining said temperature to control said polymerization, mixing saidheated gases with a hydrocarbon oil to be cracked, said hydrocarbon oilbeing heated to a temperature below its cracking temperature and saidmixture being in such proportion as to result in cracking of a part ofsaid oil passing said mixture through a cracking zone, and maintainingsaid pressure on said mixture in the cracking zone, removing thecracking mixture from said cracking zone while reducing said pressureand adding fresh feed to the mixture.

' 3. The method of cracking hydrocarbon oil to produce a high-gradeanti-knock motor fuel comprising the steps of freeing normallyincondensible hydrocarbon gases of gases rich in methane, ethane,hydrogen, carbon monoxide and dioxide, which are diiilcult to condenseand thereby separating from incondensible gases a condensible portion,compressing said condensible portion to between 500 and 3000 pounds persquare inch and heating it to a high temperature until polymerizationstarts but not over 1200 F. and preventing said temperature from risingin order to control the polymerization products, mixing saidpolymerization products with normally liquid hydrocarbon oil heated in aheating unit to a temperature below its cracking temperature and at thesame pressure as imposed on said condensible portion and in proportionsthat the temperature of the mixture causes cracking, passing saidmixture through a cracking zone, and maintaining said pressure on saidmixture in the cracking zone, removing the mixture from said crackingzone, decreasing said pressure and temperature, adding fresh feed andseparating desired compounds from the mixture.

4. ''he method of cracking hydrocarbon oil as claimed in claim 1, thestep of separating the fraction rich in methane from normallyincondensible hydrocarbon gases being carried out by compressing thegases at low temperature and in contact with gasoline as a solvent.removing the non-condensed gases and reevaporating the dissolved gases.

5. The method of cracking hydrocarbon oil as claimed in claim 3; thestep of separating the portion rich in methane, ethane, hydrogen,nitrogen, carbon monoxide and dioxide, from normally incondensiblehydrocarbon gases being carried out by compressing the gases at lowtemperature and'in contact with saturated hydrocarbon oils as a solvent,removing the non-condensed gases and reevaporating the dissolved gases.

HENRY C. PENNRICH.

